Applications of Overriding in Owner

From Andrey

Overriding in owner class can be helpful in the following situations: composing objects for collective work; customizing an object’s behavior for a particular use; propagating requests from components to aggregates; implementing control over manipulations on class members; and others. We will consider the application of overriding in owner class to the following problems:

1. The problem of dependencies.
2. The problem of notifications.
3. Code reusability.

…and to design cases:

1. Exporting a member in the interface.
2. Implementing the concept of a property in C++.

1. Problem of Dependencies. Consider class F with members a and b, belonging to classes A and B respectively. Code C1 works with class B. When changes happen to F::b, F::a must be changed. This means that B, otherwise not tied with A, must know about A's existence to send a notification (the knowledge about A is brought into B, introducing member-to-member dependency). Alternatively, B must know about F's existence, to get F to notify F::a (the knowledge about F is brought into B, introducing member-to-owner dependency). The third solution is to rewrite code C1 to work with F instead of B (the knowledge about F is brought in C1, the interface of B or its part is included in the interface of F).